Strain Gauge Pump Control Switch

ABSTRACT

A control switch incorporates a solid state transducer, a strain gauge. The transducer responds to a local environmental condition, such as fluid level, or pressure and exhibits a parameter change which can be detected as an electrical output. Control circuits coupled to the transducer can sense the parameter change and switch a source of electrical energy to a load in response thereto.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of the filing date of U.S. Provisional Application Ser. No. 60/939,453 filed May 22, 2007 and entitled “Strain Gauge Pump Switch”. The disclosure of the '453 application is incorporated herein by reference.

FIELD

The invention pertains to solid state pump control switches. More particularly, the invention pertains to such switches which incorporate a strain gauge as a transducer to convert an environment condition, such as a level of a fluid, to an electrical signal.

BACKGROUND

Various types of switches have been developed for use in turning pumps on and off in response to an external ambient condition, such as water level. Such switches tend to be used in relative harsh environments such as in tanks of water, or, sump pits which are used to collect foundation water. Other environments include industrial fluids which might be caustic or acidic, as well as high or low temperatures.

While known switches can be useful and function properly over a period of time, they are always subject to failure. Switch failures in turn translate into non-running pumps which can result in flooded commercial, industrial and residential locations. Alternately, non-running pumps can result in water supply deficiencies, or failures to supply commercial or industrial fluids for various applications.

One switch configuration has been disclosed in U.S. Pat. No. 7,307,538, issued Dec. 11, 2007, and entitled “Pump Connector System”. The '538 patent is assigned to the assignee hereof and is incorporated herein by reference.

There is an on-going need for control switches usable in such environments which exhibit greater reliability and longer lifetimes than do known switches. Preferably, such improved switches would be price competitive with known switches and readily substitutable therefore.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a switch assemblage in accordance with the invention;

FIG. 2 is a side sectional view of an exemplary switch housing as in FIG. 1;

FIG. 3 is an end view of an embodiment of a transducer in accordance with the invention; and

FIG. 4 is a block diagram of control circuits in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

While embodiments of this invention can take many different forms, specific embodiments thereof are shown in the drawings and will be described herein in detail with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention, as well as the best mode of practicing same, and is not intended to limit the invention to the specific embodiment illustrated.

Embodiments of the invention incorporate a strain gauge as a transducer to sense the presence of a fluid either through displacement, buoyancy of a structure or by fluid pressure deforming a strain gauge platform. Such embodiments can be implemented as solid state structures which can be digitally calibrated for various settings or pressure.

In one aspect of the invention, such transducers can be coupled to electronic control and switching circuitry which can switch electrical energy to activate a load, such as an electric motor for a pump. Advantageously, motor starting inrush currents are diverted away from the transducers in such embodiments. Further, such transducers can accurately respond to changing conditions, such as level or pressure, resist vibration and can withstand harsh operating environments.

The control and switching circuitry can include relatively high power semiconductor switches which are controlled by one or more programmable processors which in turn are coupled to one or more solid state transducers, preferable strain gauges. The processor(s) can digitally calibrate one or more strain gauges.

In another aspect of the invention, a solid state switch, such as a triac, can be coupled in parallel with a relay to a pump motor connector. The switch and relay can be independently controlled by control circuits in the unit. In response to signals from the strain gauge, the control circuits can bias the switch to a low impedance state to couple electrical energy to the pump connector. In this state, the switch can couple the motor start up, inrush, current without arcing or the like to the pump connector to start the motor. Once the inrush currents have subsided, for example after a time interval such as two or three seconds, the control circuits can activate the relay which changes state and provides a closed contact pair to carry the motor current as an alternate to the solid state switch. The relay contacts shunt the motor current away from the switch enabling it to cool off as needed.

When the strain gauge indicates that the lower water level has been reached, the control circuits de-energize, turn off, the relay which open circuits the motor current circuit through those contacts. Subsequently, after another time interval, such as two or three seconds, the solid state switch is biased off, or placed in a high impedance state by the control circuits. When the switch turns off it, and not the relay contacts, absorbs any turn off current or voltage transients which might otherwise cause arcing at the relay contacts. Those contacts are thus protected from electro-ablation, contact burning.

With respect to FIGS. 1-4, a pump control system 10 includes a water tight housing 12 with an open end 12 a closed by a retaining ring 14 which carries an axially movable pressure sensing plate 16. Sensing plate 16 carries a connector prong 30, best seen in FIG. 3. Housing 12 is placed in the sump along with a pump to be switched on and off.

An electrical cable 20 couples housing 12 to a double sided AC connector 22. Connector 22 carries a pump AC receptacle 22 a at one end and AC outlet prongs 22 b at the other end. In operation, a pump AC connector is plugged into receptacle 22 a. Prongs 22 b are plugged into a local utility supplied AC outlet.

Ring 14 has an annular shape with molded radial members 14-1, -2, -3, and -4. Radial member 14-4 carries an elongated, deflectable, metal plate 32 which supports a strain gauge 34. A centered perforation 36 in a free end of plate 32 receives the connector prong 30 with a friction fit and supports pressure plate 16 for axial motion in response to applied fluid pressure.

A printed circuit board 40 carries sensing and control circuits 42. Surge suppressing circuits 44 are coupled to a DC supply 46. A digital circuit regulator 48 and analog circuit regulator 50 feed digital circuits 56 and differential amplifier 52 respectively.

The differential amplifier 52 is coupled to strain gauge 34 via connectors 34 a. Movement of the plate 16 in a first direction in response to increasing fluid pressure generates a signal of a first polarity at amplifier 52. Movement of plate 16 in the opposite direction, in response to decreasing fluid pressure generates a signal of the oppose polarity at amplifier 52.

Digital control circuits 56 include a programmable processor or computer 58 a, and associated storage, random access memory, EEPROM and Flash memory indicated generally at 58 b. Software, or, control programs stored in EEPROM or Flash memory can be executed by processor 58 a in carrying out the above described switching process.

Circuits 56 can be accessed via a programming interface 58 e. A factory calibration port 58 f is also provided.

Digital output circuits 58 c are respectively coupled to Triac driver 62 a and Triac 62 b, and relay driver 64 a and relay 64 b. As described above, electrical energy from connector 22 is switched by Triac 62 b and relay 64 b to provide a switched AC output 20 c which can be coupled to pump motor 24 via pump receptacle end 22 a.

A vent tube 20 d extends from within housing 12, via cable 20 and terminates at connector 22. Tube 20 d maintains pressure in the housing 12 at local atmospheric pressure.

From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims. 

1. A switch comprising: a housing which defines an interior region; a strain gauge carried by the housing, the strain gauge has at least one variable electrical parameter, and responds to a changing, adjacent environmental condition with a detectable change in the parameter; and electrical circuitry coupled to the strain gauge and responsive to the change in parameter value to generate a control signal.
 2. A switch as in claim 1 where the environmental condition the strain gauge responds to is one of a change in fluid level, or, a change in fluid pressure.
 3. A switch as in claim 2 which includes a deformable platform which carries the strain gauge.
 4. A switch as in claim 1 where the housing defines a first end and which includes a planar member which substantially closes the first end, the planar member is located adjacent to the strain gauge.
 5. A switch as in claim 1 where the electrical circuitry includes a solid state switching element responsive to the variable electrical parameter.
 6. A switch as in claim 5 where the element has first and second states and switches therebetween in response to the variable electrical parameter.
 7. A switch as in claim 6 where the housing carries an electrical power chord with first and second ends, one end being coupled to the element.
 8. A switch as in claim 3 where the electrical circuitry includes a solid state switching element responsive to the variable electrical parameter and where the housing carries an electrical power chord with first and second ends, one end being coupled to the element.
 9. A switch as in claim 8 where the other end carries a power input plug.
 10. A switch as in claim 9 where the plug has first and second spaced apart surfaces with electrical prongs extending from one surface and with an electrical socket defined in the plug adjacent to the other surface.
 11. A switch as in claim 10 where the prongs are adapted to receive electrical energy and the socket is adapted to be releasably connectable to an electrical load.
 12. A switch as in claim 11 where the element has first and second states and switches therebetween in response to the variable electrical parameter and where in one state an electrical circuit is completed between the prongs and the socket.
 13. An assemblage comprising: an electrical cable having first and second ends; an electrical connector attached to one end; a switch assembly having a strain gauge-type transducer responsive to one of fluid level, or fluid pressure, the transducer is carried by and coupled to the other end.
 14. An assemblage as in claim 13 which includes a power supply coupled to the transducer and carried by the other end.
 15. An assemblage as in claim 13 which includes a housing carried by the other end of the cable, the housing defines an interior region with an open end, the open end is, at least in part, closed by the switch assembly.
 16. An assemblage as in claim 15 which includes an annular housing.
 17. An assemblage as in claim 16 where the annular housing includes an annular ring with a plurality of radial members which extend from the ring to a central axis thereof.
 18. An assemblage as in claim 17 where the switch assembly includes switching circuitry coupled to the other end and to the transducer.
 19. An assemblage as in claim 18 where the switching circuitry includes a solid state switch to provide a closed electrical circuit, responsive to the transducer, that extends from the first end to the second end and then back to the first end.
 20. An assemblage as in claim 19 where the connector includes a housing which carries an electrical plug and an electrical socket.
 21. An assemblage as in claim 20 which includes a pump with a connector couplable to the electrical socket.
 22. A control system for an electric motor comprising: a watertight housing; a strain gauge carried in the housing; a vent tube with first and second ends, one end is coupled to the housing and the other end extends away from the housing; control circuits coupled to the strain gauge; a relay and an electronic switch coupled to and independently controllable by the control circuits; an electrical connector for a motor, the other end of the vent tube is located adjacent to the electrical connector as is an output from the relay and the electronic switch with the control circuits sequentially placing the switch into a conducting state and then changing a state of the relay.
 23. A system as in claim 22 where the switch and the relay provide an electrical conducting path to the connector.
 24. A system as in claim 22 where the control circuits sequentially place the switch into a conducting state and then change the state of the relay to provide the electrical conducing path to the connector in response to at least one electrical signal from the strain gauge.
 25. A system as in claim 22 which includes a bridge circuit, at least one branch of the bridge circuit is coupled to the bridge circuit.
 26. A system as in claim 22 where the control circuits include a programmable processor and associated control software stored on a computer readable medium.
 27. A system as in claim 26 which includes first software that monitors at least one electrical signal from the strain gauge.
 28. A system as in claim 27 which includes second software, responsive to at least one electrical signal from the strain gauge that carries out a pump turn-on sequence.
 29. A system as in claim 28 where the pump turn-on sequence includes: causing the electronic switch to enter a low impedance state; establishing a first time interval; responsive to a termination of the first time interval, causing the relay to go from a non-conducting to a conducting state.
 30. A system as in claim 29 which includes pump turn-off software responsive to at least one electrical signal from the strain gauge.
 31. A system as in claim 30 where the pump turn-off software includes; causing the relay to return to the non-conducting state; establishing a second time interval; responsive to a termination of the second time interval, causing the electronic switch to enter a high impedance state. 